
%0 Journal Article
%A Dickson, RS 
%A Evans, GS 
%A Fallon, GD 
%T Addition of Alkynes to the Metal-Metal Double Bond in (&#951;-C<sub>5</sub>Me,<sub>5</sub>)<sub>2</sub>Rh<sub>2</sub>(µ-CO)<sub>2</sub>; Crystal and Molecular Structure of the Complex (&#951;-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>Rh<sub>2</sub>(µ-CO){µ-C(O)C<sub>2</sub>(CF<sub>3</sub>)<sub>2</sub>}.
%J Australian Journal of Chemistry
%D 1985/02/01
%V 38
%N 2
%P 273-291
%K 
%R https://doi.org/10.1071/CH9850273
%U https://www.publish.csiro.au/paper/CH9850273 
%X Various alkynes (EtC2Et, MeO2CC2CO2Me, CF3C2CF3, PhC2Ph, C6F5C2C6F5, PhC2Me, PhC2C6-F5, PhC2CO2Me) react with (&#951;-C5Me5)2Rh2(&#956;-CO)2 in acetone at room temperature; no reaction was observed with ButC2But. The &#963;-bridging alkyne complex, trans-(&#951;-C5Me5)2Rh2(CO)2(&#956;-&#951;1:&#951;1C6F5C2C6F5), was obtained from the reaction with C6F5C2C6F5. With the other alkynes, dimetallaeneone complexes, (&#951;-C5Me5)2Rh2(&#956;-CO){&#956;-&#951;2:&#951;2-C(O)C2RR&#8242;}, are formed. Some of these 'eneone' complexes co-exist with (&#951;- C5Me5)2Rh2(CO)2(&#956;-&#951;1:&#951;1-RC2R¿) in the solid state (RC2R¿ = PhC2C6F5) and/or in solution (EtC2Et, CF3C2CF3, PhC2C6F5); others (MeO2CC2CO2Me, PhC2Ph, PhC2Me, PhC2CO2Me) exist exclusively as (&#951;-C5Me5)2Rh2(&#956;-CO){&#956;-&#951;2:&#951;2- C(O)C2RR&#8242;} in both the solid and solution states. The geometry of the bridging group in (&#951;-C5Me5)2Rh2(&#956;-CO){&#956;-&#951;2:&#951;2-C(O)C2(CF3)2} has been determined from an X-ray diffraction study. The compound crystallizes with four molecules in the monoclinic space group P21/n in a unit cell of dimensions a 9.451(4), b 15.287(5), c 18.821(8)&#506;, &#946; 98.66(5)&#176;. The structure was solved by conventional heavy atom methods and refined to R 0.066 based on 4356 observed reflections above background. The structure contains a metalla-eneone ring, Rh -C(=O)-C(CF3)=C(CF3), with the alkene bond &#951;2-attached to the second rhodium atom. Variable temperature N.M.R . measurements establish that the complexes (&#951;- C5Me5)2Rh2(&#956;-CO){&#956;-&#951;2:&#951;2-C(O)C2R2}(R = CF3 or CO2Me) are fluxional in solution. Facile cleavage of a C(O)-C(R) bond enables the metalla-eneone ring to shift rapidly from one rhodium atom to the other.  Other products formed in the reactions between (&#951;-C5Me5)2Rh2(&#956;-CO)2 and RC2R&#8242; include. (&#951;-C5Me5) Rh {C4(CF3)4CO}, (&#951;-C5Me5) Rh (&#951;4-C6R6) (R = CF3 or CO2Me), (&#951;-C5Me5)2Rh2-(C4R2R&#8242;2) (R = R&#8242; = CO2Me; or R, R&#8242; = Ph, C6F5), (&#951;- C5Me5)2Rh2(CO2C2Ph2), (&#951;-C5Me5)- Rh (C4Ph4CO2), (&#951;-C5Me5)2Rh2(CO)2{C4(CF3)4}, (&#951;-C5Me5)2Rh2(CO)(&#956;-CO){COC4(C6F5)4} and C6R3R&#8242;3 (R = R&#8242; = Ph or CO2Me; R = Ph and R&#8242; = Me). Reactions between (&#951;-C5Me5)2-Co2(&#956;-CO)2 and alkynes at room temperature or above yield mononuclear cyclopentadienone  complexes (&#951;-C5Me5)Co{C4R4CO}(R = Me, CF3 or C6F5), and the mononuclear arene complex (&#951;-C5Me5)Co{C6(CF3)6}. 
